Determination of sensor operational status via sensor interrogation

ABSTRACT

A method of operating a gas sensor for a gas analyte including a sensing component includes, in a first mode, interrogating the sensor by periodically applying an electrical signal to the sensing component of the sensor, measuring sensor response to the electrical signal which is indicative of a sensitivity of the sensor each time the electrical signal is applied to the sensing component, determining whether one or more thresholds have been exceeded based upon the sensor response determined each time the electrical signal is applied to the sensing component, and entering a second mode, different from the first mode in analysis of the sensor response to the periodically applied electrical signals, if one or more thresholds are exceeded.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. Provisional Patent ApplicationSer. No. 62/738,190, filed Sep. 28, 2018, the disclosure of which isincorporated herein by reference.

BACKGROUND

The following information is provided to assist the reader inunderstanding technologies disclosed below and the environment in whichsuch technologies may typically be used. The terms used herein are notintended to be limited to any particular narrow interpretation unlessclearly stated otherwise in this document. References set forth hereinmay facilitate understanding of the technologies or the backgroundthereof. The disclosure of all references cited herein are incorporatedby reference.

Gas sensors such as electrochemical sensors have been proven over manydecades to be effective in detecting gases such as toxic gases inworkplace environments. The low cost, speed of response and selectivityof, for example, electrochemical gas sensors are just a few of thecharacteristics that have made such sensors attractive for safetyproducts. However, one of the necessary requirements for useelectrochemical gas sensor and other gas sensors has been frequentcalibration. For example, the sensitivity of an electrochemical sensoris influenced by the water content of its electrolyte, which changesover the seasons of the year, geographical location, etc. as a result offluctuations in ambient relative humidity. Such relative humidityfluctuations lead to lower sensitivities in dry regions or during dryseasons and higher sensitivities in wetter region or during wetterseasons.

Prudence thus dictates that gas detection instrumentation, includingelectrochemical gas sensors and/or other gas sensors, be testedregularly for functionality. For example, frequent calibration with atest gas having a known concentration of the analyte or target gas(including a non-zero and zero concentrations) has been required toadjust for the sensitivity changes discussed above. It is a commonpractice to, for example, perform a “bump check,” or functionality checkon portable gas detection instrumentation on a daily basis. The purposeof this test is to ensure the functionality of the entire gas detectionsystem, commonly referred to as an instrument. A periodic bump check orfunctionality check may also be performed on a permanent gas detectioninstrument to, for example, extend the period between full calibrations.Gas detection systems include at least one gas sensor, electroniccircuitry (including a power supply) to drive the sensor, interpret itsresponse and display its response to the user. The systems furtherinclude a housing to enclose and protect such components. A bump checktypically includes: a) applying a test gas of interest (usuallyincluding a known concentration of the target or analyte gas theinstrument is intended to detect or a simulant therefor to which theinstrument is responsive); b) collecting and interpreting the sensorresponse; and c) indicating to the end user the functional state of thesystem (that is, whether or not the instrument is properly functioning).

In the past, bump tests were performed regularly and, typically, daily.Bump checks provide a relatively high degree of assurance to the userthat the gas detection device is working properly. The bump checkexercises all the necessary functionalities of all parts of the gasdetection device in the same manner necessary to detect an alarm levelof a hazardous gas. In that regard, the bump check ensures that there isefficient gas delivery from the outside of the instrument, through anytransport paths (including, for example, any protection and/or diffusionmembranes) to contact the active sensor components. The bump check alsoensures that the detection aspect of the sensor itself is workingproperly and that the sensor provides the proper response function orsignal. The bump check further ensures that the sensor is properlyconnected to its associated power supply and electronic circuitry andthat the sensor signal is being interpreted properly. Moreover, the bumpcheck ensures that the indicator(s) or user interface(s) (for example, adisplay and/or an annunciation functionality) of the gas detectioninstrument is/are functioning as intended.

However, periodic/daily bump checks have a number of significantdrawbacks. For example, such bump checks are time consuming, especiallyin facilities such as industrial facilities that include many gasdetection systems or instruments. The bump check also requires the useof expensive and potentially hazardous calibration or test gases.Further, the bump check also requires a specialized gas delivery system,usually including a pressurized gas bottle, a pressure reducingregulator, and tubing and adapters to correctly supply the calibrationor test gas to the instrument. The requirement of a specialized gasdelivery system often means that the opportunity to bump check apersonal gas detection device is limited in place and time by theavailability of the gas delivery equipment.

Recently, a number of systems and methods have been proposed to reducethe number of bump tests required. Such a system may, for example,include electronic interrogation of a sensor in the absence of a testgas. The fluctuations in sensitivity of an electrochemical gas sensorarising from moisture loss or gain in a number of sensors occursgradually but in a predictable manner as the average relative humidityslowly changes. Likewise, the sensor response to an electronicinterrogation (in the absence of or without application of a test gasincluding a known concentration of the analyte gas or a substitutetherefor) changes in a similar manner. An electronic interrogation may,for example, be used to measure sensitivity changes and correct forthem. Such electronic interrogation techniques and resulting correctionsfor electrochemical gas sensors are, for example, disclosed in U.S. Pat.Nos. 7,413,645, 7,959,777, 9,784,755, and 9,528,957, and in U.S. PatentApplication Publication Nos. 2013/0186777 and 2017/0219515, thedisclosures of which are incorporated herein by reference. In suchelectronic interrogation approaches, an electrical signal such as apotential pulse is typically applied to a sensing element or componentof the sensor and the resulting response is measured and recorded. Aresponse may, for example, be measured in the form of, for example, amaximum peak (current) value (MPV) or and/or another parameter. Theseresponses are compared to values taken during a previous gas test/pulsecycle. Changes from the calibration values may be correlated to changesin sensor sensitivity.

Various electronic interrogation techniques have also been developed forsensors other than electrochemical sensors (such as combustible gassensors). For example, U.S. Patent Application Publication No.2014/0273263, the disclosure of which is incorporated herein byreference, discloses periodic measurement of a variable related toreactance of a sensing element of a combustible gas sensor to determinethe operational status of the sensing element. U.S. patent applicationSer. Nos. 15/597,933 and 15/597,859 disclose electronic interrogationtechniques for combustible gas sensors in which a variable related tothe mass of a sensing element (for example, an electrical property suchas resistance) is periodically measured to determine if, for example,substances such as inhibitors or poisons have been deposited on thesensing element.

Although, current testing or interrogation techniques are valuable indetermining if an individual sensor is in a functional state ofoperation at the time of testing, relatively little success has beenachieved in predicting future failure of such sensors.

SUMMARY

In one aspect, a method of operating a gas sensor for a gas analyteincluding a sensing component includes, in a first mode, interrogatingthe sensor by periodically applying an electrical signal to the sensingcomponent of the sensor, measuring sensor response to the electricalsignal which is indicative of a sensitivity of the sensor each time theelectrical signal is applied to the sensing component, determiningwhether one or more thresholds have been exceeded based upon the sensorresponse determined each time the electrical signal is applied to thesensing component, and entering a second mode, different from the firstmode in analysis of the sensor response to the periodically appliedelectrical signals, if one or more thresholds are exceeded.

In a number of embodiments, the sensor response to the periodicallyapplied electrical signals in the second mode is analyzed to determineif the sensor response to the periodically applied electrical signals isstabilizing. The method may, for example, further including determininga rate of change of the sensor response during the second mode todetermine if the sensor response to the periodically applied electricalsignals is stabilizing. In a number of embodiments, at least one of amagnitude and a direction of the rate of change of the sensor responseis determined. In a number of embodiments, the method further includeschanging the one or more thresholds after determining that the sensorresponse to the periodically applied electrical signals has stabilized.There is no need to apply any test gas during electronic sensorinterrogation. In that regard, the sensor response may be determinedwithout application of a test gas to the sensor. In a number ofembodiments, at least one of a magnitude and a direction of the rate ofchange of the sensor response is determined.

The sensor may, for example, be an electrochemical gas sensor and thesensing component may, for example, be a working electrode of theelectrochemical gas sensor. A value for the sensor response may, forexample, be determined on the basis of at least one defined parameter ofthe sensor response. In a number of embodiments, the at least onedefined parameter of the sensor response is selected from the group of amaximum current peak value, an area under a current curve, a minimumpeak value, a peak-to-peak value, a reverse area under the curve, abaseline value of the sensor response or functions or one or morethereof (for example, products, ratios or more complex functions of oneor more of such parameters). The value for the sensor response at eachof the periodically applied electronic interrogations may, for example,be a change in the value at least one defined parameter of the sensorresponse measure at each of the periodically applied electronicinterrogations from a value thereof determined at a calibration of thesensor.

In a number of embodiments, the one or more threshold values for thesensor response are determined by tracking a value of the sensorresponse over time and determining an upper threshold and a lowerthreshold of nominal behavior for the sensor. In a number ofembodiments, the one or more threshold values for the sensor responseare determined by tracking the sensor response over time for a pluralityof like sensors and determining a group upper threshold and a grouplower threshold of nominal behavior for the plurality of sensors. In anumber of embodiments in which group thresholds are determined, one ormore other threshold values are determined by tracking the sensorresponse of each of the plurality of like sensors over time anddetermining an individual upper threshold and an individual lowerthreshold of nominal behavior for each of the plurality of like sensors.The second mode may, for example, be entered for each of the pluralityof like sensors based upon a comparison the sensor response of each ofthe plurality of like sensors to the group upper threshold and the grouplower threshold as well as to the individual upper threshold and theindividual lower threshold.

The sensors of the plurality of like sensors hereof may, for example,exhibit at least one common characteristic other than being a likesensor. The at least one common characteristic may, for example, be ageographical area of deployment or a range of time of manufacture.Groups and subgroups of like sensor may be established in a number ofembodiments.

In a number of embodiments, data from the sensor is transmitted to aremote processor system for processing and/or analysis. In a number ofembodiments, data or information from a second gas sensor for a secondgas analyte different from the gas analyte or data from a third sensorfor an environmental condition is transmitted to the gas sensor.

In another aspect, a system includes a sensor including a sensingcomponent having at least one property sensitive to an analyte, andcircuitry in operative connection with the sensing component. Thecircuitry is configured, in a first mode, to interrogate the sensor byperiodically applying an electrical signal to the sensing component,measuring a sensor response to the electrical signal which is indicativeof a sensitivity of the sensor each time the electrical signal isapplied to the sensing component, and compare the sensor response to oneor more threshold values. The circuitry is further configured todetermine, based upon the comparison of sensor response to the one ormore threshold values, whether to enter a second mode, different fromthe first mode in analysis of sensor response to the periodicallyapplied electrical signals, if one or more thresholds are exceeded.

In a number of embodiments, the circuitry is configured to analyze thesensor response to the periodically applied electrical signals in thesecond mode to determine if the sensor response to the periodicallyapplied electrical signals is stabilizing. The circuitry may, forexample, be further configured to determine a rate of change of thesensor response during the second mode to determine if the sensorresponse to the periodically applied electrical signals is stabilizing.At least one of a magnitude and a direction of the rate of change of thesensor response may, for example, be determined. In a number ofembodiments, the circuitry is further configured to change the one ormore thresholds after determining that the sensor response to theperiodically applied electrical signals has stabilized. The circuitrymay, for example, be configured to determine the sensor response withoutapplication of a test gas to the sensor.

In a number of embodiments, the sensor is an electrochemical gas sensorand the sensing component is a working electrode of the electrochemicalgas sensor. As described above, a value for the sensor response isdetermined on the basis of at least one defined parameter of the sensorresponse. In a number of embodiments, the at least one defined parameterof the sensor response is selected from the group of a maximum currentpeak value, an area under a current curve, a minimum peak value, apeak-to-peak value, a reverse area under the curve, a baseline value ofthe sensor response, or a function or functions of one or more thereofdescribed above. The value for the sensor response at each of theperiodically applied electronic interrogations may, for example, be achange in the value at least one defined parameter of the sensorresponse measure at each of the periodically applied electronicinterrogations from a value thereof determined at a calibration of thesensor.

In a number of embodiments, the one or more threshold values for thesensor response are determined by tracking a value of the sensorresponse over time and determining an upper threshold and a lowerthreshold of nominal behavior for the sensor. In a number ofembodiments, the one or more threshold values for the sensor responseare determined by tracking the sensor response over time for a pluralityof like sensors and determining a group upper threshold and a grouplower threshold of nominal behavior for the plurality of sensors. Eachof the plurality of like sensors may, for example, include acommunication system to transmit data regarding the sensor response tothe periodically applied electronic interrogations and to receive dataregarding the group upper threshold and the group lower threshold ofnominal behavior for the plurality of sensors. In a number ofembodiments wherein group thresholds are determined, one or more otherthreshold values are determined by tracking the sensor response of eachof the plurality of like sensors over time and determining an individualupper threshold and an individual lower threshold of nominal behaviorfor each of the plurality of like sensors. The second mode may, forexample, be entered for each of the plurality of like sensors based upona comparison the sensor response of each of the plurality of likesensors to the group upper threshold and the group lower threshold aswell as to the individual upper threshold and the individual lowerthreshold.

In a number of embodiment in which a plurality of like sensors aretracked, each of the plurality of like sensors has at least one commoncharacteristic other than being a like sensor. The at least one commoncharacteristic may, for example, be a geographical area of deployment ora range of time of manufacture.

Data from the sensor(s) may, for example, be transmitted to a remoteprocessor system for processing and/or analysis. Data or informationfrom a second gas sensor for a second gas analyte different from the gasanalyte or data from a third sensor for an environmental condition istransmitted to the gas sensor.

In a further aspect, a method of operating a system including aplurality of like gas sensors, wherein each of the plurality of like gassensors includes a sensing component, includes, in a first mode,interrogating each of the plurality of like gas sensors by periodicallyapplying an electrical signal to the sensing component of the sensor,determining a sensor response to the electrical signal which isindicative of a sensitivity for each of the plurality of like gassensors each time the electrical signal is applied to the sensingcomponent thereof, and analyzing the sensor response of each of theplurality of like gas sensors to the periodically applied electricalsignals based upon a nominal response of the plurality of like gassensors to the periodically applied electrical signals determined overtime. The method may, for example, further include determining whetherto enter a second mode, different from the first mode in analysis of thesensor response to the periodically applied electrical signals, for eachof the plurality of like gas sensors based upon comparison of the sensorresponse of each of the plurality of like gas sensors to the nominalresponse of the plurality of like gas sensors in the first mode. Themethod may be further characterized as described above.

In still a further aspect, a system includes a plurality of like gassensors, wherein each of the plurality of like gas sensors includes asensing component and electronic circuitry in operative connection withthe sensing component. The electronic circuitry is configured, in afirst mode, to interrogate each of the plurality of like gas sensors byperiodically applying an electrical signal to the sensing component ofthe sensor, to determine a sensor response to the electrical signalwhich is indicative of a sensitivity for each of the plurality of likegas sensors each time the electrical signal is applied to the sensingcomponent thereof, and to analyze the sensor response to theperiodically applied electrical signals based upon a nominal response ofthe plurality of like gas sensors to the periodically applied electricalsignals determined over time. The electronic circuitry of each of theplurality of like sensors may, for example, be further configured todetermine whether to enter a second mode, different from the first modein analysis of the sensor response to the periodically appliedelectrical signals, based upon comparison of the sensor response to thenominal response of the plurality of like gas sensors in the first mode.The system may be further characterized as described above.

The present devices, systems, and methods, along with the attributes andattendant advantages thereof, will best be appreciated and understood inview of the following detailed description taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates schematically an embodiment of an electrochemicalsensor hereof.

FIG. 1B illustrates a schematic circuit diagram of an embodiment of asensor hereof.

FIG. 1C illustrates a representative response to an electronicinterrogation of an electrochemical gas sensor.

FIG. 1D illustrates the response of FIG. 1C with an enlarged scale.

FIG. 2 illustrates a change, after initial calibration, in sensorresponse (a maximum peak (current) value or MPV) to electronicinterrogations over time.

FIG. 3 illustrates the change, after initial calibration, in sensorresponse (MPV) to an electronic interrogations over time for multiplesensors.

FIG. 4 illustrates the change, after initial calibration, in sensorresponse (set forth as the difference between a change in MPV and theaverage change in MPV) to an electronic interrogation over time formultiple sensors.

FIG. 5 illustrates the change, after initial calibration, in sensorresponse (MPV) to electronic interrogations over time for a singlesensor which briefly drops below a threshold of −3 standard deviationbut subsequently recovers.

FIG. 6 illustrates the change, after initial calibration, in sensorresponse (set forth as the difference between a change in MPV and theaverage change in MPV) to an electronic interrogation over time formultiple sensors, wherein the output of one of the sensors is changingin a manner different from the others but it's output is still in thenominal range.

FIG. 7 illustrates a representative embodiment of a system for datacommunication, processing and analysis for sensor data from one or morefacilities or locations.

DETAILED DESCRIPTION

It will be readily understood that the components of the embodiments, asgenerally described and illustrated in the figures herein, may bearranged and designed in a wide variety of different configurations inaddition to the described representative embodiments. Thus, thefollowing more detailed description of the representative embodiments,as illustrated in the figures, is not intended to limit the scope of theembodiments, as claimed, but is merely illustrative of representativeembodiments.

Reference throughout this specification to “one embodiment” or “anembodiment” (or the like) means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment. Thus, the appearance of the phrases “in oneembodiment” or “in an embodiment” or the like in various placesthroughout this specification are not necessarily all referring to thesame embodiment.

Furthermore, described features, structures, or characteristics may becombined in any suitable manner in one or more embodiments. In thefollowing description, numerous specific details are provided to give athorough understanding of embodiments. One skilled in the relevant artwill recognize, however, that the various embodiments can be practicedwithout one or more of the specific details, or with other methods,components, materials, et cetera. In other instances, well knownstructures, materials, or operations are not shown or described indetail to avoid obfuscation.

As used herein and in the appended claims, the singular forms “a,” “an”,and “the” include plural references unless the context clearly dictatesotherwise. Thus, for example, reference to “processor” includes aplurality of such processors and equivalents thereof known to thoseskilled in the art, and so forth, and reference to “the processor” is areference to one or more such processors and equivalents thereof knownto those skilled in the art, and so forth. Recitation of ranges ofvalues herein are merely intended to serve as a shorthand method ofreferring individually to each separate value falling within the range.Unless otherwise indicated herein, and each separate value, as well asintermediate ranges, are incorporated into the specification as ifindividually recited herein. All methods described herein can beperformed in any suitable order unless otherwise indicated herein orotherwise clearly contraindicated by the text.

The terms “electronic circuitry”, “circuitry” or “circuit,” as usedherein include, but is not limited to, hardware, firmware, software orcombinations of each to perform a function(s) or an action(s). Forexample, based on a desired feature or need. a circuit may include asoftware controlled microprocessor, discrete logic such as anapplication specific integrated circuit (ASIC), or other programmedlogic device. A circuit may also be fully embodied as software. As usedherein, “circuit” is considered synonymous with “logic.” The term“logic”, as used herein includes, but is not limited to, hardware,firmware, software or combinations of each to perform a function(s) oran action(s), or to cause a function or action from another component.For example, based on a desired application or need, logic may include asoftware controlled microprocessor, discrete logic such as anapplication specific integrated circuit (ASIC), or other programmedlogic device. Logic may also be fully embodied as software.

The term “processor,” as used herein includes, but is not limited to,one or more of virtually any number of processor systems or stand-aloneprocessors, such as microprocessors, microcontrollers, centralprocessing units (CPUs), and digital signal processors (DSPs), in anycombination. The processor may be associated with various other circuitsthat support operation of the processor, such as random access memory(RAM), read-only memory (ROM), programmable read-only memory (PROM),erasable programmable read only memory (EPROM), clocks, decoders, memorycontrollers, or interrupt controllers, etc. These support circuits maybe internal or external to the processor or its associated electronicpackaging. The support circuits are in operative communication with theprocessor. The support circuits are not necessarily shown separate fromthe processor in block diagrams or other drawings.

The term “controller,” as used herein includes, but is not limited to,any circuit or device that coordinates and controls the operation of oneor more input and/or output devices. A controller may, for example,include a device having one or more processors, microprocessors, orcentral processing units capable of being programmed to performfunctions.

The term “logic,” as used herein includes, but is not limited to.hardware, firmware, software or combinations thereof to perform afunction(s) or an action(s), or to cause a function or action fromanother element or component. Based on a certain application or need,logic may, for example, include a software controlled microprocess,discrete logic such as an application specific integrated circuit(ASIC), or other programmed logic device. Logic may also be fullyembodied as software. As used herein, the term “logic” is consideredsynonymous with the term “circuit.”

The term “software,” as used herein includes, but is not limited to, oneor more computer readable or executable instructions that cause acomputer or other electronic device to perform functions, actions, orbehave in a desired manner. The instructions may be embodied in variousforms such as routines, algorithms, modules or programs includingseparate applications or code from dynamically linked libraries.Software may also be implemented in various forms such as a stand-aloneprogram, a function call, a servlet, an applet, instructions stored in amemory, part of an operating system or other type of executableinstructions. It will be appreciated by one of ordinary skill in the artthat the form of software is dependent on, for example, requirements ofa desired application, the environment it runs on, or the desires of adesigner/programmer or the like.

A number of embodiments hereof are discussed in connection withelectrochemical gas sensors and electronic interrogation thereof.However, the devices, systems and methods hereof are applicable to anytype of sensor in which diagnostic testing or electronic interrogationof a sensing component is performed.

As described above, recent development for electronic interrogation ofelectrochemical sensors have diminished the requirement for frequentcalibrations with test gas. In an electronic interrogation, anelectrical signal is applied to a sensing component of the sensor whichinteracts with the target or analyte gas. For example, an electricalsignal may be applied to a working electrode of an electrochemicalsensor which includes an electrocatalyst which catalyzes a reduction oroxidation reaction with the analyte gas. Likewise, an electrical signalmay be applied to a sensing element of a combustible gas sensor whichmay or may not include a catalyst which facilitates combustion of ananalyte gas (for example, by providing a reaction pathway with a loweractivation energy than a non-catalyzed reaction) upon heating of thesensing element to a suitable temperature.

In the case of electrochemical gas sensors, electronic interrogationsmay, for example, be of fairly short duration to minimize the amount oftime a sensor is offline to conduct sensor testing diagnostics (that is,during a sensor electronic interrogation cycle). In a number ofrepresentative embodiments of, for example, electrochemical gas sensordevices, systems and/or methods for electronic interrogation may allowfor a return to a normal (gas sensing) mode operation for theelectrochemical sensors hereof that is under 10 seconds, under 5 secondsor even under 1 second. The devices, systems and methods for electronicinterrogation of sensor not only allow an instrument including one ormore sensors to remain “online”, but also provide for active, automaticsensor status monitoring as a background operation, without therequirement of user initiation. The electronic interrogations hereofoccur periodically. As used herein, the term periodically refers toelectronic interrogation which occur from time to time or multiple timesover time but not necessarily at a fixed interval or frequency. Thefrequency of the electronic interrogations may be constant or may vary.Providing for sensor interrogation at a frequency of, for example,several times an hour can provide for nearly constant sensor life andhealth status monitoring.

In an electrochemical gas sensor, the gas to be measured typicallypasses from the surrounding atmosphere or environment into a sensorhousing through a gas porous or gas permeable membrane to a firstelectrode or working electrode (sometimes called a sensing electrode)where a chemical reaction occurs. A complementary chemical reactionoccurs at a second electrode known as a counter electrode (or anauxiliary electrode). The electrochemical sensor produces an analyticalsignal via the generation of a current arising directly from theoxidation or reduction of the analyte gas (that is, the gas to bedetected) at the working electrode. A comprehensive discussion ofelectrochemical gas sensors is also provided in Cao, Z. and Stetter, J.R., “The Properties and Applications of Amperometric Gas Sensors,”Electroanalysis, 4(3), 253 (1992), the disclosure of which isincorporated herein by reference.

The working and counter electrode combination produces an electricalsignal that is (1) related to the concentration of the analyte gas and(2) sufficiently strong to provide a signal-to-noise ratio suitable todistinguish between concentration levels of the analyte gas over theentire range of interest. In other words, the current flow between theworking electrode and the counter electrode must be measurablyproportional to the concentration of the analyte gas over theconcentration range of interest.

In addition to a working electrode and a counter electrode, anelectrochemical sensor often includes a third electrode, commonlyreferred to as a reference electrode. A reference electrode is used tomaintain the working electrode at a known voltage or potential. Thereference electrode should be physically and chemically stable in theelectrolyte.

Electrical connection between the working electrode and the counterelectrode is maintained through the electrolyte. Functions of theelectrolyte include: (1) to efficiently carry the ionic current; (2) tosolubilize the analyte gas; (3) to support both the counter and theworking electrode reactions; and (4) to form a stable referencepotential with the reference electrode. Criteria for an electrolyte may,for example, include the following: (1) electrochemical inertness; (2)ionic conductivity; (3) chemical inertness; (4) temperature stability;(5) low cost; (6) low toxicity; (7) low flammability; and (8)appropriate viscosity.

In general, the electrodes of an electrochemical cell provide a surfaceat which an oxidation or a reduction (a redox) reaction occurs toprovide a mechanism whereby the ionic conduction of the electrolytesolution is coupled with the electron conduction of the electrode toprovide a complete circuit for a current. The measurable current arisingfrom the cell reactions of the electrochemical cell is directlyproportional to the extent of reaction occurring at the electrode.Preferably, therefore, a high reaction rate is maintained in theelectrochemical cell. For this reason, the counter electrode and/or theworking electrode of the electrochemical cell generally include anappropriate electrocatalyst on the surface thereof to support thereaction rate.

As a result of electrostatic forces, the volume of solution very closeto the working electrode surface is a very highly ordered structure.This structure is important to understanding electrode processes. Thevolume of solution very close to the electrode surface is variouslyreferred to as the diffusion layer, diffuse layer, and or the Helmholtzlayer or plane.

The magnitudes of the resistance and capacitance present in anelectrochemical cell are a result of the nature and identities of thematerials used in its fabrication. The resistance of the electrolyte isa result of the number and types of ions dissolved in the solvent. Thecapacitance of the electrode is primarily a function of the effectivesurface area of the electrocatalyst. In an ideal world, these quantitiesare invariant. However, the solution resistance present in anamperometric gas sensor that utilizes an aqueous (water-based)electrolyte may change, for example, as a result of exposure todifferent ambient relative humidity levels. As water transpires from thesensor, the chemical concentration of the ionic electrolyte increases.This concentration change can lead to increases or decreases in theresistivity of the electrolyte, depending on the actual electrolyteused.

Moreover, even for substances normally thought of as insoluble in aparticular solvent, there is a small, but finite concentration of thesubstance in the solvent. For example, there is a very small, but finiteconcentration of metal from the electrodes dissolved in the electrolyteof an electrochemical sensor. This small concentration of dissolvedmetal is constantly in flux. That is, metal atoms are constantlydissolving from the electrode and then replating somewhere else. The neteffect of this process is to decrease the effective surface area of theelectrode. This has the effect of lowering the sensor capacitance overtime. Both of the above-described effects have the net effect ofchanging the sensitivity of the sensor over its lifetime.

FIG. 1A illustrates a schematic diagram of a representative embodimentof an electrochemical sensor 10 which may be used in the devices,systems and methods hereof. Sensor 10 includes a housing 20 having a gasinlet 30 for entry of one or more target gases or analyte gases intosensor 10. In the illustrated embodiment, electrolyte saturated wickmaterials 40 a, 40 b and 40 c separate a working electrode 50 from areference electrode 70 and a counter electrode 80 within sensor 10and/or provide ionic conduction therebetween via the electrolyte 44within housing 20 and absorbed within wick materials 40 a, 40 b and 40c. Electronic circuitry 100 as known in the art is provided, forexample, to maintain a desired potential difference between workingelectrode 50 and reference electrode 70, to vary or pulse the potentialdifference as described herein, and to process an output signal fromsensor 10.

In the illustrated embodiment, working electrode 50 may be formed by,for example, depositing a first layer of catalyst 54 on a diffusionmembrane 52 (using, for example, catalyst deposition techniques known inthe sensor arts). Gas readily transfers or transports (via, for example,diffusion) through diffusion membrane 52, but electrolyte 44 does notreadily transfer or transport therethrough. Working electrode 50 may beattached (for example, via heat sealing) to an inner surface of a top,cap or lid 22 of housing 20.

Electronic circuitry 100 may, for example, include a processor orcontroller system 102 including one or more processors ormicroprocessors to control various aspects of the operation of sensor10. A memory system 104 may be placed in operative or communicativeconnection with processor system 102 and may store software for controlof sensor 10 and/or analysis of the output thereof as described herein.A user interface system (including, for example, a display, speakeretc.) may also be placed in operative or communicative connection withprocessor system 102. A communication system 108 such as a transceivermay be placed in operative or communicative connection with processorsystem 102 for wired and/or wireless communication. A power source 110(for example, a battery system) may provide power for electroniccircuitry 100.

FIG. 1B illustrates schematically an embodiment of a portion or part ofelectronic or control circuitry 100 used in a number of studies of thesensors hereof. The portion of electronic circuitry 100 illustrated inFIG. 1B is sometimes referred to as a potentiostatic circuit. In athree-electrode sensor as illustrated in FIG. 1A, a predeterminedpotential difference or voltage is maintained between referenceelectrode 70 and sensing or working electrode 50 to control theelectrochemical reaction and to deliver an output signal proportional tothe current produced by the sensor. As described above, workingelectrode 50 responds to the analyte or target gas by either oxidizingor reducing the gas. The redox reaction creates a current flow that isproportional to the gas concentration. Current is supplied to sensor 10through counter electrode 80. A redox reaction opposite to that of thereaction at the working electrode takes place at counter electrode 80,completing the circuit with working electrode 50. The potential ofcounter electrode 80 is allowed to float. When gas is detected, the cellcurrent rises and counter electrode 80 polarizes with respect toreference electrode 70. The potential on counter electrode 80 is notimportant, as long as the circuit provides sufficient voltage andcurrent to maintain the correct potential of working electrode 50.

As, for example, described in U.S Patent Application Publication No.2017/0219515, in a number of representative embodiments, the measuringcircuit for electrical/electronic circuitry 100 includes a single stageoperational amplifier or op amp IC1. The sensor current is reflectedacross a gain resistor 120 (having a resistance of 5 kΩ in theillustrated embodiment), generating an output voltage. A load resistor122 (having a resistance of 56Ω in the illustrated embodiment) may bechosen, for example, via a balance between the fastest response time andbest signal-to-noise ratio.

A control operational amplifier IC2 provides the potentiostatic controland provides the current to counter electrode 80 to balance the currentrequired by working electrode 50. The inverting input into IC2 isconnected to the reference electrode but does not draw any significantcurrent from the reference electrode.

During electronic interrogation of an electrochemical gas sensor hereofsuch as sensor 10, a non-faradaic current may be induced (for example,via application of energy to working electrode 50). For example, anelectrical signal may be applied to working electrode 50 such that astep change in potential is created which generates a non-faradaiccurrent. The generated non-faradaic current can be used to monitor thesensor operational status, functionality or health as a result of thecharging of the electrodes. However, as described above, the sensor issubsequently returned to its normal bias potential or potential rangefor normal operation in sensing a target or analyte gas. The process ofreturning the sensor to its operating bias or operating potentialdifference (which may be zero) produces a current peak (a chargebuild-up) in the opposite direction. The current peak arising on returnto the operating potential difference can take many seconds todissipate.

Information regarding sensor health, operational status or operationalstate may be obtained from a response to an electronic interrogationmeasured in the form of, for example, (i) a maximum peak value (MPV),which is the maximum current observed upon the application of thepotential pulse; (ii) an area under the curve (AUC), which is theintegrated current response of the working electrode after theapplication of the potential pulse (this is equivalent to the chargingresponse of the sensor; (iii) minimum peak value (mPV), which is theminimum current obtained upon removal or reversal of the potentialpulse, ordinarily as the difference in current observed immediatelyafter and immediately before the removal or reversal of the potentialpulse, though it can also be tabulated and used as the differencebetween the minimum current and the baseline; (iv) peak-to-peak value(PP), which is the algebraic difference between the maximum and minimumobserved currents; (v) reverse area under the curve (rAUC), or, moreaccurately, the area under the reverse curve, which is the chargingcurrent obtained by integrating the current response after the removalor reversal of the potential pulse; (vi) change in a baseline orbaseline output and functions thereof (for example, products, ratiosand/or more complex functions of one, two or more such parameters). Theoperational state of a sensing component (for example, a workingelectrode of an electrochemical gas sensor or a sensing element of acombustible gas sensor) and the sensor/sensor device is typicallydetermined by relating such parameters and/or other parameters tochanges in sensitivity of the sensor. Sensitivity refers to the ratio ofthe output signal (for example, current) and the physical quantitymeasured (for example, concentration of analyte or target gas).

Measuring/analyzing single data points or multiple data points overshort time spans provides a response/current versus time curve as, forexample illustrated in FIGS. 1C and 1D for a representativeelectrochemical gas sensor for hydrogen sulfide or H₂S. A rapiddischarge of even relatively large current peaks arising when inducing anon-faradaic current in sensor 10 (or another sensor hereof) and/or inreturning sensor 10 (or another sensor hereof) to its operatingpotential difference may be achieved via active control of sensorelectronic circuitry or electronics 100 (for example, by decreasing aload resistance in electronic circuitry 100 between working electrode 50and the point at which the output/response is measured after the testpotential difference has been applied). In a number of embodiments, theload resistance between working electrode 50 and the output ofoperational amplifier IC1 is decreased to a low value. Subsequently, theload resistance between working electrode 50 and the output ofoperational amplifier IC1 is restored to its normal or operational loadresistance (or to within an operation range of load resistance) afterthe charge is substantially dissipated or fully dissipated.

In a number of embodiments, load resistor 122 (see FIG. 1B) is bypassedto decrease the load resistance between working electrode 50 and theinverting terminal of operational amplifier IC1. A bypass circuit 124may, for example, be provided to bypass load resistor 122. In a numberof embodiments, a field effect transistor (FET) 126 was used as a switchin a bypass circuit 124 to controllably effect a bypass or short circuitaround load resistor 122. In a number of embodiments, ametal-oxide-semiconductor FET or MOSFET was used.

FIGS. 1C and 1D illustrate the output of a representative sensor 10including a working electrode 50 designed to detect hydrogen sulfide orH₂S. In the studied embodiment of FIGS. 1C and 1D, working electrode 50was formed by depositing an iridium catalyst on a diffusion membrane,reference electrode 70 was formed by depositing an iridium catalyst on adiffusion membrane, and counter electrode 80 was formed by depositing aniridium catalyst on a diffusion membrane. The bias potential oroperating potential difference of the sensor was 0 mV. As illustrated inFIG. 1C, at a time represented by point A, an electronic interrogationprocedure is initiated. After 0.5 seconds (represented by point B), atest potential difference is applied. In the illustrated studies, a testpotential of +10 mV was applied. A maximum peak value (MPV) of outputwas recorded 1/16^(th) of a second after application of the testpotential as represented by point C. At that time, the potential wasalso returned to the operating potential difference of 0 mV. Inbypassing load resistor 122, FET 126 was activated at generally the sametime or contemporaneously with return of the potential to the operatingpotential difference. The significantly lower load resistance causes asignificant negative current spike (which would be viewed as a very highnegative gas ppm reading in the normal mode of operation). However, therapid discharge which occurs upon bypassing load resistor 122 returnsthe sensor output to the baseline in a very short period of time (thatis, in less than 1 second). The scale is expanded in FIG. 1D to betterillustrates this result. It, however, takes many seconds for the outputto return to the baseline output when load resistor 122 is not bypassed.As illustrated in FIG. 1C, when FET 126 is deactivated and 56Ω loadresistor 122 is restored in the circuit at a time of approximately 0.95seconds as represented by point D, the output current is below a valuethat would be discerned by the end user. This value is typically in therange of approximately 0 to ±2 ppm of the target gas

Information regarding sensor health or the state of the sensor may beobtained maximum peak (current) value (MPV) and/or another parameter asdescribed above upon application of an electrical signal in, forexample, the form of an electrode potential change that is quite smalland/or short in duration, and measuring/analyzing single data points ormultiple data points over short time spans in a resultantresponse/current curve. In a number of representative embodimentshereof, MPV is used to characterize the sensing element/workingelectrode of an electrochemical sensor. As described above, a rapiddischarge of even relatively large current peaks arising when inducing anon-faradaic current in sensor 10 (or another electrochemical sensorhereof) and/or in returning sensor 10 (or another sensor hereof) to itsoperating potential difference may be achieved via active control ofsensor electronics/electronic circuitry 100 (for example, by decreasinga load resistance in electronic circuitry 100 between working electrode50 and the point at which the output/response is measured after the testpotential difference has been applied). In a number of embodiments, theload resistance between working electrode 50 and the output ofoperational amplifier IC1 is decreased to a low value. Subsequently, theload resistance between working electrode 50 and the output ofoperational amplifier IC1 is restored to its normal or operational loadresistance (or to within an operation range of load resistance) afterthe charge is substantially dissipated or fully dissipated.

The fluctuations in sensitivity of an electrochemical sensor as a resultof, for example, moisture loss or gain occur gradually, but in agenerally predictable manner, as the average relative humidity slowlychanges. The sensor response to a gas-less, electronic interrogationsuch as described above changes in a similar manner. Electronicinterrogation may be used to track sensitivity changes and to correctfor sensitivity changes as described in, for example, U.S. Pat. Nos.7,413,645, 7,959,777, 9,784,755, and 9,528,957, and in U.S. PatentApplication Publication Nos. 2013/0186777 and 2017/0219515. As describedabove, a potential pulse is typically applied to the sensing componentof the sensor and the resulting response is recorded, for example, inthe form of a maximum peak (current) value and/or one or more otherparameters. These responses may be compared to values taken during aprevious gas test/pulse cycle. Changes from calibration values arecorrelated to changes in operational status/sensor sensitivity. In thisway, a sensor's health at the time of interrogation is evaluated. Thesensitivity may then be adjusted to correct for such changes. Suchmethodologies provide a real-time status of the sensor's health at thetime of the interrogation but do not address future sensor performance.

In a number of embodiments of devices, systems and methods hereofmultiple, consecutive interrogation events are performed in a first modeor first interrogation mode to, for example, determine if a sensorresponse to the electronic interrogation is outside of nominal behavior.For example, changes in value one or more variables based upon ordetermined from one or more parameters such as MPV, AUC and/or otherparameters may be used to evaluate when a sensor is need offurther/altered analysis and/or maintenance. If, for example, a sensor'sresponse to interrogation is outside of a nominal, normal or expectedvariation (for example, expected variation as a result of normal,gradual changes in relative humidity), that sensor may be identified orflagged as needing attention.

In a number of embodiments hereof, once a sensor exhibits a response toan electronic interrogation that is outside of a nominal range ofresponse, a second mode, second interrogation mode or observe mode isentered. In the second mode, analysis of the response of the sensor toelectronic interrogation is different than in the first mode. Thesampling rate of one or more parameters may be altered and/or theidentity of the one or more parameters measured may change in the secondmode. In a number of embodiments, a determination is made over one ormore periods of time in the second mode from the measured response toperiodic electronic interrogations (that is, multiple electronicinterrogations over time) if the response of the sensor to theelectronic interrogations is stable or stabilizing. It may, for example,be determined over one or more periods of times in the second modewhether the sensor response is approaching an average rate of changewithin a defined threshold or remaining within a determined or definedrange of response over the one or more periods of time in the secondmode. In a number of embodiments, a rate of change in a measuredvariable (based upon or derived from one or more parameters) may, forexample, be determined over one or more periods of time in the secondmode to determine if the sensor response is stabilizing. A determinationregarding sensor response stability (for example, as determined from amagnitude/direction of a rate of change over one or more periods of timein the second mode) may be used to determine, for example, if sensorsetting should be changed (for example, changing nominal response range,changing sensitivity compensation; etc.), if a recalibration of thesensor is needed or if the sensor needs to be replaced. In the devices,systems and methods hereof, a sensor's health or operational status(that is, sensitivity) is not only gauged at the instant of theelectronic interrogation, its future health is estimated using anaggregate of health measurements (that is, measured responses toelectronic interrogations).

The nominal range of sensor response to electronic interrogation may bederived in a number of ways. A straightforward manner of determining thenominal range of response is to track the response of the sensor over aperiod of time to determine nominal or normal variation. Limits (forexample, an upper threshold and a lower threshold) may then be set toidentify or flag deviations in sensor behavior. Such limits may, forexample, be redetermined over time as further electronic interrogationsare carried out. The nominal limits or thresholds and whether suchnominal limits have been exceeded (thereby triggering entry of thesecond mode) hereof may, for example, be determined via software storedin memory system 104 and executable by processor system 102. An exampleis displayed in FIG. 2, wherein the change in MPV value from the initialcalibration point (at time of manufacture) is plotted over 80+ days.

In FIG. 2, a sensor exhibiting the nominal behavior is labeled sensor 10a(i). The average over the 80+ days of the study of FIG. 2 is 26 countswith a standard deviation of 107 counts. Limits or thresholds may, forexample, be established using, a multiple of the standard deviation (forexample, between ±1 to ±3 sigma). In the illustrated embodiment, limitswere established using ±3 times the standard deviation to capture 99.7%of the nominal distribution. Such limits (upper and lower thresholds)are denoted by the upper and lower dashed traces in FIG. 2. In a firstmode as described above, delta MPV is tracked over time and compared tothe nominal delta MPV values (that is, the upper and lower thresholds ofnominal delta MPV values). Once the delta MPV moves beyond one of thoselimits, the system may, for example, enter the second mode or observemode wherein analysis of the response of the electronic interrogation isdifferent than in the first mode. As described above, the rate of changeof the delta MPV may be tracked over one or more time periods in thesecond mode to determine if the sensor response to the electronicinterrogations is stabilizing. Thus, in a number of embodiments of thesecond mode, electronic interrogation continues as described above andthe delta MPV is still tracked, but the rate of change of the delta MPV(dΔMPV/dt) is also tracked.

Two representative examples of tracking the rate of change of the deltaMPV are illustrated in FIG. 2. The data trace of sensor 10 a(ii)indicates that the sensor has experienced a step change in MPV value.Once the delta MPV has moved beyond the −3 sigma value/limit, the rateof change is monitored in the second mode of operation as describedabove. Further, an alert or notification may (but need not) be providedto the user to alert the user that the sensor has entered into thesecond mode. However, it may not be necessary that the user take anyaction at that time. Providing a second mode or observe mode asdescribed herein may provide significant benefits by decreasing theinteraction required of a user as compared to currently availablesensors by reducing unnecessary interactive maintenance. Depending uponthe control software saved in memory system 104 of the sensor, thesensor, may, for example, change compensation, increase the frequency ofpulse/electronic interrogation tests, measure one or more additionalparameters, change the range of nominal sensor response, etc. in thesecond mode. Such action may, for example, be automated or not requireuser intervention.

In the case of a sensor in which a response to electronic interrogationis found to stabilize in the second mode (via, for example, electronicor electrical circuitry 100), that response may stabilize within theoriginal range of nominal response or within a different or offset rangeof nominal response. One or more limits or thresholds for acceptableresponse/nominal response for a sensor may be defined. If a sensorstabilizes to a response range outsize of such a limit or threshold, thesensor may, for example, be flagged for service or replacement. In thecase of sensor 10 a(ii), the rate of change stabilizes, and the systempredicts that the future state of sensor 10 a(ii), while offset from theoriginal range or nominal response, will be stable within a new,acceptable nominal range. The system may, for example, trigger a“recalibrate sensor” indication or alert and/or re-set the system in itsnew state. In the case of “new” calibration, the sensor may, forexample, determine delta MPV from a new “anchor” value determined duringthe new calibration. The sensor may also (alternatively or additionally)continue to determine delta MPV from the calibration at the time ofmanufacture.

On the other hand, the data trace of sensor 10 a(iii) indicates acatastrophic failure of sensor 10 a(iii). Again, once the delta MPVexceeds the −3 sigma lower limit, the rate of change may, for example,be monitored over one or more time periods in the second mode todetermine if the sensor's response to electronic interrogation becomesstable. In the case of sensor 10 a(iii), the sensor response (delta MPVin this example) continues to rapidly change and the system predictsthat sensor 10 a(iii) will rapidly move out of its useful state for gasdetection. The system may, for example, trigger a “replace sensor”alert. Having made such a determination, a quantitation may beperformed, and an alert provided to take the sensor out of operationeither permanently or for a period of time (for example, 24 hours or anumber of days) if a repair is possible. One may replace the sensorduring that time if the out of service period is excessively dangerousor burdensome.

“Group” nominal ranges of response to electronic interrogation may alsobe determined using a data distribution over a population of sensors(for example, a plurality of like sensors) which may, for example, shareat least one common characteristic other than being a like sensor. Asused herein, the term “like” refers to sensors manufactured in a similaror the same manner. In general, such sensors are manufactured to sensethe same analyte and include a sensing component manufactured in thesame manner. For example, like electrochemical gas sensor for a specificgas analyte may include working electrodes manufactured in a similar orsame manner and include the same electrolyte. A counter electrode, areference electrode and/or electronic circuitry of such sensors may alsobe manufactured in a similar or same manner. Such electrochemical gassensor may, for example, be two- or three-electrode sensors as known inthe art. Like combustible gas sensors may, for example, include asensing element, a compensating element and/or electronic circuitrymanufactured in a similar or the same manner.

With respect to a common characteristic (other than being a like sensor)the population of sensors may, for example, share the same localenvironment and/or a common range of manufacture date/time. Such sensorscould be units all used at the same location of a particular customer orall units used in a larger area (a city or county for instance). Thedistribution could also, for example, be based on sensor manufacturedate code and cover a global and/or a localized population. Groups andsubgroups of like sensor may be established based upon differing sharedor common characteristics. The results from each unit may be compiled,and the distribution of the entire population may be used as the nominaldata set.

FIG. 3 illustrates a representative example of data from 15 sensors inthe same local environment. As described above, the change in MPV valuefrom the initial calibration point is plotted for all sensors over 80+days. The average over the 80+ days was 5 counts with a standarddeviation of 117 counts. In the representative example of FIG. 3, grouplimits or thresholds may, for example, be established using a multipleof sigma. In the illustrated embodiment, group upper and lowerthresholds were established using ±3 times the standard deviation tocapture 99.7% of the nominal distribution. Group limits may, forexample, be determined via a processor system external to the pluralityof like sensors which is in communication with each of the plurality oflike sensors to received data/information therefrom. The determinedgroup limits may, for example, be transmitted from the externalprocessing system to each of the plurality of like sensor. Such grouplimits are denoted by upper and lower dashed lines in FIG. 3. Once ameasured delta MPV for a particular sensor moves to beyond these limits,the sensor system can enter a second mode or observe mode. As describedabove, in a number of embodiments, the rate of change of the delta MPVcan be tracked for a sensor in the second mode to determine if sensorresponse will stabilize. Similar to FIG. 2, two examples are provided inFIG. 3 for a sensor step change (sensor 10 a(ii)) and a catastrophicsensor failure (sensor 10(iii)). The actions for such individual sensors(for example, adjusting nominal thresholds or initiation ofnotifications/alerts such a “re-calibration alert” and a “replacesensor” alert) may, for example, be the same as described above inconnection with the single sensor example of FIG. 2.

Referring again to FIG. 3, it is apparent that the studied localpopulation of sensors responds in a similar manner to the day-to-daychanges in the local environment. This result suggests an additionaltreatment using the local population data to compare each sensor's dailydelta MPV value with the average daily delta MPV for all the sensors inthat local population. In this way, the nominal behavior for thepopulation is normalized for each interrogation event and deviationsfrom nominal behavior are more apparent. FIG. 4 illustrates thismethodology. The average over the 80+ days is 0 counts, but the standarddeviation is now only 55 counts. Again, group limits can be establishedusing ±3 times the standard deviation to capture 99.7% of the nominaldistribution. These are denoted by the dashed traces in FIG. 4. Thisdata treatment removes a portion of the day to day noise in the deltaMPV value and makes the two deviation cases to become more easilydiscernible from the other sensors.

Some sensors may exhibit more inherent noise than the generalpopulation. A sensor that is flagged by the population treatmentdiscussed in connection with FIG. 3 (that is, upon comparison of thesensor response to one or more electronic interrogations to group limitsor thresholds determined for the population/plurality of like sensors)may still be operating nominally when compared to its own history (thatis, upon comparison of the sensor response to one or more electronicinterrogations to individual limits or thresholds determined for theindividual sensor). In light of that and other cases, the treatmentdiscussed in connection with FIG. 3 can be combined with the singlesensor treatment discussed in connection with FIG. 2. In therepresentative example of FIG. 4, sensor 10 a(iv) shows a few instancesof dropping below the −3 standard deviation/threshold line for thegroup/plurality of like sensors being monitored. Sensor 10 a(iv) may,for example, be identified of flagged for a follow-up single treatmentor evaluation. FIG. 5 illustrates a single sensor treatment (asdescribed, for example, in connection with FIG. 2 above) for sensor 10a(iv). As illustrated in FIG. 5, sensor 10 a(iv) briefly drops below the−3 standard deviation limit for the individual sensor but recovers. Bycombining both a group, population or distribution treatment and anindividual sensor treatment as described herein, a more comprehensiveevaluation is obtained and sensor 10 a(iv) may, for example, be deemedto be functioning adequately.

When evaluating trends over a population of, for example, like sensorsthat share at least one common characteristic (that is, a commoncharacteristic other than being a like sensor; for example, geographiclocation, manufacture date range, etc.) data analysis other thandetermination of whether a measured value is outside of a nominal rangemay be performed. One may, for example, expect (based upon data from asensor population) that a particular sensor should be stabilizing orfollowing a certain trend, but the particular sensor may be exhibitoutput that is different from its peers or other sensors in themonitored population. Such differences may, for example, be exhibited inmanner other than output of a particular value/parameter (for example,MPV or delta MPV) outside of a threshold range (for example, outside+/−3std. deviation). One may, for example, determine/analyze the magnitudeof response, the magnitude of the rate of change and/or the direction ofchange of each sensor relative to peers. As illustrated in FIG. 6,sensor 10 a(v) is exhibiting a rate of change in delta MPV that isopposite that of the other sensors in the studied population. Sensor 10a(v) may, for example, be identified or flagged and placed in a secondor observe mode for further/alternative analysis and/or evaluation basedon such a trend, which is different from its peers, even though thedelta MPV behavior is within in the nominal range for the population ofsensor and/or for individual sensor 10 a(v).

In a number of embodiments, in the case that it is determined in thesecond mode that, for example, a particular sensor should berecalibrated and/or that its nominal range of response should be offsetby at least a defined or predetermined amount from the nominal range ofa population/plurality of like sensors of which the particular sensor isa member, it may, for example, be determined that the particular sensorshould no longer be tracked as a member of the population/plurality oflike sensors. If the particular sensor stabilizes within the nominalrange of the population/plurality of like sensors or only slightlyoffset therefrom, it may, for example, be determined that the particularsensor should be continued to be tracked as a member of thepopulation/plurality of like sensors and it's response may continue tobe considered in determining the group nominal thresholds for thepopulation/plurality of like sensors.

In the case of monitoring population/plurality of like sensors, a sensorresponse or response trend different from its peers or other sensors inthe monitored population/plurality of like sensors may not be anindication that the sensor at issue is malfunctioning but may be anindication that the sensor should not be a member of the monitoredpopulation/plurality of like sensors. Such a different response may, forexample, result from a different microenvironment in a particularlocation. For example, the sensor of the monitored population/pluralityof like sensor exhibiting a different response/trend may be locatedwithin a structure at a particular location, while the other sensors ofthe population/plurality of like sensors may be positioned out of doors.Similarly, the sensor of the monitored population/plurality of likesensor exhibiting a different response/trend may be located withindirect sunlight while the other sensors of the population/plurality oflike sensors are not. Thus, a response of a sensor that differs fromthat of its peers in a population/plurality of like sensor may triggeran investigation of whether the sensor in properly included in thepopulation/plurality of like sensors. It may, for example, be determinedthat the sensor under investigation should be monitored onlyindividually or within another population/plurality of like sensors.

In addition to providing further information/guidance in analyzing theresponse of one or more sensors, tracking the response to periodicelectronic interrogations of a population/plurality of like sensors may,for example, provide information regarding a systemic issue with thesensors of the population/plurality of like sensors. Such sensors may,for example, have been manufactured in a determined date/time ormanufacture code range. Certain defects (for example, a defect inelectrolyte composition) may not be discovered at the time ofmanufacture but may result in anomalous response to electronicinterrogations thereafter. Tracking of the response of such a pluralityof like sensors to electronic interrogation may, for example, result indetection of a systemic problem with the sensors even before such adefect becomes otherwise apparent.

Changes in maximum peak value and/or one or more other parameter fromthe time of manufacture of a sensor (and/or from another starting oranchor point, such as a subsequent calibration) until later in asensor's life may be analyzed to, for example, determine what type ofenvironmental conditions the sensor has experienced over that historicalperiod (for example, low humidity or drying conditions). Based on suchhistorical data, one may change one or more parameters of sensoroperation. A software algorithm stored in memory and executable by oneor more processors may, for example, apply a different temperaturecompensation. An algorithm may, for example, apply a differentsensitivity compensation based on such historical data. An algorithmhereof (based on such historical data) may, for example, be used toalter nominal response range based on such historical data.

Data from sensors that that are not like sensors or sensors that havevery different characteristics than one or more sensors beingmonitored/analyzed may also be used in determining the operationalstatus of the sensor(s) in the devices, systems and methods hereof. Suchsensors that are not like sensors may, for example, be sensors that arefor an analyte other than the sensor(s) for which the operational statusis being determined. Such sensors that are not like sensors may, forexample, be a different type of sensor (for example, a combustible gassensor in the case that the like sensors are electrochemical gassensors).

Moreover, sensors for environmental conditions such as pressure sensors,humidity sensors, altitude sensors or altimeters, etc. may also oralternatively be used in determining operational status. Data fromtemperature and/or humidity sensors may, for example, be used indetermining appropriate nominal ranges for a measured parameter (forexample, delta MPV as described in representative examples hereof).Different settings may be established for sensor locations that are coldand dry than those that are hot and humid. Altitude may, for example, berelated to an oxygen concentration which affects the output of oxygensensors as well as combustible gas sensors. At high altitude, theconcentration of oxygen is lower than at sea level (fewer molecules ofoxygen are present per unit volume). Below sea level, for example, in anunderground mine, the environment may be rich in oxygen.

For example, in the case the operational status of one or morecombustible gas sensors is being tracked under a methodology hereof, anoxygen sensor may be used to determine the combustible gas sensor(s)is/are operating in a condition of oxygen deficiency or oxygen excessover a particular time period. Such an oxygen sensor may, for example,be an electrochemical gas sensor. Likewise, sensors for inhibitorsand/or poisons for combustible gas sensors (for example,sulfur-containing compounds, halogens, silicon-containing compoundsetc.) may be sensed by, for example, electrochemical and/or othersensors.

In the case the operational status of one or more electrochemical gassensors is being tracked under a methodology hereof, a combustible gassensor or other sensor may, for example, be used to detect interferentgases for the electrochemical gas sensor(s). Alcohols may, for example,be detected via a combustible gas sensor. Speciation, as disclosed, forexample, U.S. Pat. No. 10,234,412, the disclosure of which isincorporated herein by reference, may be used in detecting a species ofalcohol. Alcohols may affect certain electrochemical gas sensor such ascarbon monoxide or CO sensors. Even a small increase in a combustiblegas sensor output may be associated in time with anomalous output froman electrochemical gas sensor for CO sensor or even with such a sensorgoing offline. Alkenes may also be detected via combustible gas sensors.Alkenes are similarly interferents for electrochemical gas sensors forCO. Using data from one or more combustible gas sensors, one maydetermine if an alkene us present which is causing a response in one ormore CO sensors.

The timespan of history or data from one or more gas sensors, pressuresensors, humidity sensors, temperature sensors etc. may be analyzed todetermine how such a data history may be affecting the performance ofone or more sensor monitored under the methodologies hereof. Locationdata (for example, from GPS or other systems) and the location of amonitored sensor or sensors in a facility may, for example, becorrelated with gas test data, anomalies, alarms, up-scale readings,down-scale readings etc. Determination and/or analysis of nonstandardconditions or occurrences can be associated with the output of amonitored sensor or sensors.

Various types of gas sensors may include one or more filters to, forexample, limit or prevent gas sensing elements from coming into contactwith or being exposed to an inhibitor, poison, interferent etc. Changesin the transport properties of such filters upon exposure to such aninhibitor, poison, interferent etc. may affect sensor response. Sensorssensitive to an inhibitor, poison, interferent etc. for a sensor orsensors being monitored using a methodology hereof may, for example, beused in interpreting output trends in such sensor(s). Likewise, suchsensors sensitive to an inhibitor, poison, interferent etc. may be usedto monitor or track the operational status of a filter for a sensor orsensors being monitored using a methodology hereof.

FIG. 7 illustrates a representative embodiment of a system forcollection, communication and analysis of data from one or multiplesensors which may, for example, be located at a single facility ordistributed over multiple facilities. In a number of embodiments hereof,a facility 200 a (for example, an oil refinery, off-shore drilling rig,manufacturing facility, industrial chemical plant etc.) includes one ormore sensor 10 a(i) through 10 a(vii) hereof, while one or more otherfacilities represented by facility 200 b includes one or more othersensors 10 b(i) through 10 b(vii) hereof. Although seven sensors areillustrated in each of facilities 200 a and 200 b, facilities mayinclude fewer or more sensors. Some facilities may, for example, include100 or more sensors. Operation of the system components of facility 200b (and/or other facilities) with respect to data collection,communication and/or processing is very similar to the components offacility 200 a. Data communication and/or processing in the systemshereof is, therefore, primarily discussed below in connection withfacility 200 a.

As described above each sensor 10 a(i) hereof includes a communicationsystem (for example, transceiver) which may be wired or wireless. Datafrom sensors 10 a(i) through 10 a(vii) may, for example, be communicateddirectly to a remote processing system 500, which is discussed furtherbelow. Data from sensors 10 a(i) through 10 a(vii) may alternatively betransmitted to remote system 500 via a local system 250 a. In a numberof embodiments, data may, for example, be communicated from sensors 10a(i) through 10 a(vii) to local system 250 a via local network 220 awhich may, for example, include a 4 to 20 milliamp (mA) transmissionsystem as known in the art, an ethernet-based network, and/or a wirelessnetwork. Data may, for example, be collected and transmitted inreal-time to remote system 500 for analysis. Data transfer may beperformed in a continuous or a discontinuous/batch manner. For example,raw sensor data or processed sensor data may be transmitted by localsystem 250 a to remote system 500 for processing (or further processing)and/or analysis by remote system 500. Remote system 500 can receiveddata from many local systems 250 a, 250 b etc. (that is, from manydifferent facilities). Local system 250 a may, for example, include aprocessing system 252 a (including, for example, one or more processorsor microprocessors), an associated memory system 254 a in communicativeconnection with processor system 252 a and a communication system 256 ain communicate connection with processor system 252 a.Processing/analysis may, for example, be distributed in the processingsystems of the sensors, the local systems and remote system 500 (forexample, in determining group upper thresholds and lower thresholds).Transmission from sensors 10 a(i) through 10 a(vii) and/or local system250 a to remote system 500 occur through a network 400 which may includewired and/or wireless communication protocols (for example, via cellphone transmission protocols, internet transmission protocols, data viatelephone wire protocols etc.)

Remote system 500 may, for example, include a central processing systemor a distributed processing system that may, for example, include one ormore computers, servers or server systems 510. Computer(s), server(s) orserver system(s) 510 may, for example, include one or more processors orprocessor systems 512 which are in communicative connection with one ormore memory or storage systems 514 as known in the computer arts. Memorysystem(s) 514 may include one or more databases 516 stored therein.Local systems 250 a, 250 b etc. may communicate with a communicationsystem or systems 520 of remote system 500 through one or more wired orwireless communication channels 400 (for example, landline telephones,wireless telephones, a broadband internet connection and/or othercommunication channel(s)) as described above. Software stored in memorysystem(s) 514 or in one or more other memory system in communicativeconnection with processor(s) 512 may be used to process or analyze datafrom local systems 250 a, 250 b etc.

The foregoing description and accompanying drawings set forth a numberof representative embodiments at the present time. Variousmodifications, additions and alternative designs will, of course, becomeapparent to those skilled in the art in light of the foregoing teachingswithout departing from the scope hereof, which is indicated by thefollowing claims rather than by the foregoing description. All changesand variations that fall within the meaning and range of equivalency ofthe claims are to be embraced within their scope.

What is claimed is:
 1. A method of operating a gas sensor for a gas analyte including a sensing component, comprising: in a first mode, interrogating the sensor by periodically applying an electrical signal to the sensing component of the sensor, measuring sensor response to the electrical signal which is indicative of a sensitivity of the sensor each time the electrical signal is applied to the sensing component, determining whether one or more thresholds have been exceeded based upon the sensor response determined each time the electrical signal is applied to the sensing component, and entering a second mode, different from the first mode in analysis of the sensor response to the periodically applied electrical signals, if one or more thresholds are exceeded.
 2. The method of claim 1 wherein the sensor response to the periodically applied electrical signals in the second mode is analyzed to determine if the sensor response to the periodically applied electrical signals is stabilizing.
 3. The method of claim 2 further comprising determining a rate of change of the sensor response during the second mode to determine if the sensor response to the periodically applied electrical signals is stabilizing.
 4. The method of claim 2 further comprising changing the one or more thresholds after determining that the sensor response to the periodically applied electrical signals has stabilized.
 5. The method of claim 1 wherein the sensor response is determined without application of a test gas to the sensor.
 6. The method of claim 3 wherein at least one of a magnitude and a direction of the rate of change of the sensor response is determined.
 7. The method of claim 3 wherein the sensor is an electrochemical gas sensor and the sensing component is a working electrode of the electrochemical gas sensor.
 8. The method of claim 7 wherein a value for the sensor response is determined on the basis of at least one defined parameter of the sensor response.
 9. The method of claim 8 wherein the at least one defined parameter of the sensor response is selected from the group of a maximum current peak value, an area under a current curve, a minimum peak value, a peak-to-peak value, a reverse area under the curve, a baseline value of the sensor response or a function of one or more thereof.
 10. The method of claim 8 wherein the value for the sensor response at each of the periodically applied electronic interrogations is a change in the value of at least one defined parameter of the sensor response measured at each of the periodically applied electronic interrogations from a value thereof determined at a calibration of the sensor.
 11. The method of claim 2 wherein the one or more threshold values for the sensor response are determined by tracking a value of the sensor response over time and determining an upper threshold and a lower threshold of nominal behavior for the sensor.
 12. The method of claim 2 wherein the one or more threshold values for the sensor response are determined by tracking the sensor response over time for a plurality of like sensors and determining a group upper threshold and a group lower threshold of nominal behavior for the plurality of like sensors.
 13. The method of claim 12 wherein one or more other threshold values are determined by tracking the sensor response of each of the plurality of like sensors over time and determining an individual upper threshold and an individual lower threshold of nominal behavior for each of the plurality of like sensors.
 14. The method of claim 13 wherein the second mode is entered for each of the plurality of like sensors based upon a comparison the sensor response of each of the plurality of like sensors to the group upper threshold and the group lower threshold as well as to the individual upper threshold and the individual lower threshold.
 15. The method of claim 7 wherein the one or more threshold values for the sensor response are determined by tracking a value of the sensor response over time and determining an upper threshold and a lower threshold of nominal behavior for the sensor.
 16. The method of claim 7 wherein the one or more threshold values for the sensor response are determined by tracking the sensor response over time for a plurality of like sensors and determining a group upper threshold and a group lower threshold of nominal behavior for the plurality of like sensors.
 17. The method of claim 16 wherein one or more other threshold values are determined by tracking the sensor response of each of the plurality of like sensors over time and determining an individual upper threshold and an individual lower threshold of nominal behavior for each of the plurality of like sensors.
 18. The method of claim 17 wherein the second mode is entered for each of the plurality of like sensors based upon a comparison the sensor response of each of the plurality of like sensors to the group upper threshold and the group lower threshold as well as to the individual upper threshold and the individual lower threshold.
 19. The method of claim 16 wherein each of the plurality of like sensors has at least one common characteristic other than being a like sensor.
 20. The method of claim 19 wherein the at least one common characteristic is a geographical area of deployment or a range of time of manufacture.
 21. The method of claim 1 wherein data from the sensor is transmitted to a remote processor system for analysis.
 22. The method of claim 1 wherein data from a second gas sensor for a second gas analyte different from the gas analyte or data from a third sensor for an environmental condition is transmitted to the gas sensor.
 23. A system, comprising: a sensor comprising a sensing component having at least one property sensitive to an analyte; and circuitry in operative connection with the sensing component configured in a first mode to interrogate the sensor by periodically applying an electrical signal to the sensing component, measuring a sensor response to the electrical signal which is indicative of a sensitivity of the sensor each time the electrical signal is applied to the sensing component, compare the sensor response to one or more threshold values, the circuitry further being configured to determine, based upon the comparison of sensor response to the one or more threshold values, whether to enter a second mode, different from the first mode in analysis of sensor response to the periodically applied electrical signals, if one or more thresholds are exceeded.
 24. A method of operating a system including a plurality of like gas sensors, each of the plurality of like gas sensors including a sensing component, comprising: in a first mode, interrogating each of the plurality of like gas sensors by periodically applying an electrical signal to the sensing component of the sensor, determining a sensor response to the electrical signal which is indicative of a sensitivity for each of the plurality of like gas sensors each time the electrical signal is applied to the sensing component thereof, and analyzing the sensor response of each of the plurality of like gas sensors to the periodically applied electrical signals based upon a nominal response of the plurality of like gas sensors to the periodically applied electrical signals determined over time.
 25. The method of claim 24 further comprising determining whether to enter a second mode, different from the first mode in analysis of the sensor response to the periodically applied electrical signals, for each of the plurality of like gas sensors based upon comparison of the sensor response of each of the plurality of like gas sensors to the nominal response of the plurality of like gas sensors in the first mode. 